1. Field of the Invention
The present invention relates to a dry etching apparatus for etching substrates such as silicon substrates for producing semiconductor integrated circuits by utilizing a gas plasma generated by radiofrequency glow discharge.
2. Description of the Prior Art
Dry etching apparatuses for etching object substrates (hereinafter referred to in brief as "substrates") by utilizing radiofrequency glow discharge are widely used in the field of production of semiconductor integrated circuits These dry etching apparatuses usually have a structure comprising a vacuum chamber provided therein with an RF electrode, to which a radiofrequency voltage is to be applied, and with a grounding electrode between which and the RF electrode a plasma is to be generated. Various etching systems are respectively employed in these dry etching apparatuses. Increasingly used in various processes for producing semiconductor devices, since they are capable of anisotropic etching and excellent in mass productivity are reactive ion etching (RIE) apparatuses wherein etching is effected while a substrate is placed on an RF electrode.
The early models of RIE apparatuses have a structure wherein an object substrate having thereon an etching mask made of a photoresist is merely placed on an RF electrode (or a substrate bed disposed thereon). This structure allows the substrate to be readily heated by a plasma to a high temperature, thereby causing thermal damage to the photoresist of the etching mask and deterioration of the etching pattern. Therefore, this structure is defective in that improving the etching rate and controlling the etching pattern as desired are difficult.
In view of the above, there have been proposed some methods of keeping a substrate at a desirable low temperature during an etching treatment. One of the methods mechanically clamps a substrate on an RF electrode (or a substrate bed disposed thereon) to improve the thermal contact therebetween to thereby keep the temperature of the substrate low. Another method involves passing a gas such as He between the reverse surface of a substrate and the upper surface of a substrate bed to enhance heat dissipation from the substrate to thereby keep the temperature of the substrate low. Yet another method (electrostatic chucking) provides a DC electrode under a substrate bed (or an RF electrode) to produce therewith an electrostatic force which brings a substrate into close contact with the substrate bed or (the RF electrode) to improve heat transfer therebetween to thereby keep the temperature of the substrate low. Particularly, since the last-mentioned electrostatic chucking method involves a relatively simple structure and provides a large cooling effect, various systems for realizing electrostatic chucking have been proposed.
For example, Japanese Patent Publication No. 53,853/1981 (Japanese Patent Laid-Open No. 90,228/1980) discloses a "dry etching apparatus" wherein the electrostatic chucking method is employed through utilization of the electrical conductivity of a gas plasma. According to this conventional system, an RF electrode and a gas plasma serve as electrodes sandwiching a dielectric film therebetween not only to make the system simple but also to minimize the damage to a substrate. Further, according to this system, an electrostatic chucking force is exerted only during the existence of the gas plasma to facilitate chucking and unchucking of the substrate. Thus, this system for electrostatic chucking is very effective. FIG. 1 is a schematic cross-sectional view of the structure of the dry etching apparatus disclosed in the above-mentioned publication. The structure of FIG. 1 comprises a radiofrequency power source 101, an RF electrode 102, substrates 103, a counter electrode 104, and a dielectric film 105 on which the substrates 103 to be electrostatically chucked are placed. The structure of FIG. 1 further comprises an insulator 106, a DC power source 107, a radiofrequency cutoff circuit 108, a radiofrequency matching circuit 109, a conductive rubber sheet 110 provided on the RF electrode 102, a plasma 111, cooling system 112 for the RF electrode 102, a vacuum chamber 113, a pumping system 114, and a gas feed system 115. The above-mentioned components 101 to 115 of the structure are all well known in the art, and hence the detailed description thereof is omitted.
However, various problems arose when etching was effected with dry etching apparatuses of the kind as described above In the case of a batch type dry etching apparatus comprising an RF electrode 102 having an oversized (in area) upper surface for the purpose of carrying out a blanket etching treatment of a plurality of substrates where a conductive rubber sheet 110 provided all over the broad upper surface of the RF electrode 102, a it is very difficult to cover the entire surface of the rubber sheet 110 exposed in vacuum chamber 113 with a dielectric film 105 such that the latter would be in perfect close contact with the former without leaving spaces therebetween. Even if the above-mentioned entire surface of rubber sheet 110 can be covered with dielectric film 105 without leaving spaces therebetween, small spaces do develop between the dielectric film 105 and the rubber sheet 110 when the vacuum chamber 113 is evacuated to a high degree of vacuum. Thus, when plasma is generated, abnormal discharge would occur in these small spaces, thereby not only causing failure in the electrostatic chucking but also destroying the dielectric film 105 and/or DC power source 107.
Usually, substrate 103 is electrostatically chucked by an electrostatic force produced by a potential difference between a negative self-bias voltage of several hundreds volts induced in substrate 103 during etching and a DC voltage applied to RF electrode 102 and, hence, to conductive rubber sheet 110 provided thereon. Accordingly, a positive DC voltage of about 1 kV is applied from a DC power source 107 to RF electrode 102. The aforementioned abnormal discharge results from such applied voltage of about 1 kV, which, during plasma discharge, forces electrons in the plasma to flow through the small spaces as mentioned above into the RF electrode 102 to cause abnormal discharge.
Even when the DC voltage for electrostatic chucking is reversed from a positive polarity to a negative polarity, such abnormal discharge occurs as well. In this case, ions would flow into the above-mentioned small spaces.
In order to avoid the occurrence of such abnormal discharge, the inventors of the present invention proposed an apparatus as shown in FIG. 2 (Japanese Patent Laid-Open No. 149,734/1982). In this apparatus, a plurality of substrate beds (supports) 214 are provided on an RF electrode 213 having a surface covered indirectly with a shield panel 211 and directly with a dielectric electrode cover 212. Electrodes 217 each covered with a dielectric film 215 and insulated from the RF electrode 213 with a dielectric layer 216 provided therebetween are embedded only just under the corresponding substrate beds 214. A DC voltage is applied from a DC power source 218 through a radio frequency filter 219 only to these electrodes 217. The apparatus further comprises substrates 220, a counter electrode 221, an insulator 222, a radio frequency power source 223, a radio frequency cutoff circuit 224, a cooling system 225, a vacuum chamber 226, a pumping system 227, and a gas feed system 228. The foregoing apparatus is defective not only in that difficulty is experienced in wiring for DC voltage application, but also in that the etching characteristics for substrates 220 vary from substrate to substrate because of influences thereon of slight structural and like differences between the plurality of the substrate beds 214 provided on the RF electrode 213 as shown in FIG. 2.
Further, in the case of either type of the conventional apparatuses having the aforementioned respective structures as shown in FIGS. 1 and 2, even if the electrode(s) 102, 217 can be covered with the dielectric film(s) 105, 215 perfectly in close contact relation, the dielectric film(s) 105, 215 would deteriorate during dry etching. This requires frequent replacement of the dielectric film(s) 105, 215 with a new dielectric film(s), which presents an additional problem of large losses of time and labor needed for such replacement. Even when the dielectric film(s) 105, 215 is adhered to the electrode(s) 102, 217, whether or not the adhesion of the dielectric film(s) 105, 215 to the electrode(s) 102, 217 can withstand practical use cannot be estimated before an actual trial of a dry etching operation in vacuum, and the probability of successful adhesion is low. Therefore, it is problematic to adopt these dry etching apparatuses in actual large-scale integrated circuit production lines.
The present invention has been made with a view to solving the foregoing problems. Accordingly, an object of the present invention is to provide a novel dry etching apparatus wherein a substrate bed(s) having a comparatively simple structure and dielectric members are assembled into an RF electrode structure capable of sufficiently strong, electrostatically chucking of a substrate(s) on the substrate bed(s) and at the same time stably and sufficiently cooling the substrate(s) during dry etching to thereby effect the etching of the substrate(s) with excellent uniformity and reproducibility.